Behaviour wise, goats and sheep in the same pasture make a lot of sense. They get along well
enough, once they work out their misunderstandings due to different body language cues. Because goats and sheep prefer to eat different plants, you can get more out of your
land by having the two different species on the same pasture at the same time.
The other posters are giving good advice, albeit a bit generic. There are a lot more nuances to minerals than most people realize. In general, an old breed like shetland or other kinds who are descended from Finn Sheep, have sufficient copper needs and tolerances to live with goats and goat minerals, in some situations. If you are willing to do the research there is a lot of good that can be done with minerals - and even more harm if you don't do it right. If you don't have time to observe your livestock several times a day, then it's probably best to stick with the generic advice.
But if you want to know a bit more...
Most of what I'm saying here is from Pat Coleby's book Natural Sheep Care. The rest is from personal experience and consulting with
local vets and livestock gurus. It is by no means universally accepted, especially these days as there is a huge movement towards buying pre-mixed mineral supplements; many people no longer feel the need to learn the ins and outs of how minerals work.
First off,
sheep will die without copper! Sheep in general have a very narrow range where the copper consumption is healthy for them. Too little copper and they become parasite prone, have poor wool quality, some other stuff and death. Too much copper cause bad things and death. Each breed has a different range of healthy copper. For example, Icelandic and Shetlands have a very broad range, Black Welsh Mountain have very broad and high copper needs, Mernio has a higher need than say a southdown, but an extremely narrow range. This range has narrowed dramatically in the last 40 years or so due in part to breeding but more to how the pastures and
hay fields have been fertilized. Chemical fertilizer changes how the sheep (and other mammals) take up the minerals, which makes an over-dose of copper more likely.
When it comes to having animals that thrive, as opposed to just live, on your land, there is of the utmost importance that they have the proper minerals they need. Sheep and goats both depend on the proper balance of minerals, which changes on the time of year, rainfall, feed, soil make up, and so on. Sure, a goat or a sheep will produce well enough with commercial minerals, which is enough for most people. The wrong balance of minerals can reduce
milk production, increase the susceptibility to parasites and flystrike (lack of copper in BOTH sheep and goats will do this), produce poor grade wool, and of
course toxicity and mineral deficiencies.
Most mineral mixes are made for a region or even for the national 'needs' of the animal. Our local sheep mix is made with very low Selenium because most of our province has high Se in the soil. If the sheep has too much Se then it can cause copper deficiency, hoof problems, and death. Too little Se causes an increase of mastitis (Not yet common knowledge so I'm citing my local goat guru who has done extensive work researching this and is consulted by vets all over the world), increase in parasite load, change in skin/wool/hair, reproductive problems like prolapse, and of course muscle paralysis and death. Feeding the commercially prepared mineral mix to our sheep causes the death, disease and discomfort of our sheep, even though this mineral mix is made specifically for our 'region', it is not sufficient for where we live.
We have some of our sheep living up the road a little bit, and their mineral needs are very different than the ones on our own land. Even this little difference in the makeup of the soil is enough that they need different minerals to thrive.
When it comes to minerals, location is a big thing.
Shetland sheep have a much higher tolerance for copper and other minerals/diets than modern breeds of sheep. They actually have a much higher requirement for copper than sheep 'officially' do. This of course will vary depending on your land, their feed, and other elements - like if their feed has been given chemical based fertilizer which will upset the balance of minerals and other nutrients their body can use. DEPENDING on your soil, and many other factors, it is LIKELY (but NOT certain) that the shetlands MAY thrive on the goat minerals. That's a very highly qualified statement, and there is so much it depends on that one has to know a lot more about your individual situation than I do.
When in doubt, gather up some local livestock gurus - Weigh any advise they give against the health of their flock.
